Crystal field excitations in the defect-fluorite Dy2Zr2O7 and Ho2Zr2O7

The low energy physics in rare-earth oxides is largely determined by the single ion properties of the magnetic atom. We propose to measure the crystalline electric field (CEF) properties of the most common by-product of pyrochlores. Defect-fluorite is the generic name given to 2-2-7 stoichiometry compounds that, for different reasons, do not form in the Fd-3m space group. Because of their close relationship in titanate pyrochlores (spin ices), we chose here to investigate the CEF of Dy2Zr2O7 and Ho2Zr2O7. The former was recently shown to present spin dynamics down to 500 mK, in stark contrast with the canonical spin ice Dy2Ti2O7. Given that the tetrahedra arrangement and rare-earth distances in deferct-fluorites are, relative to pyrochlores, basically unaltered, the reason for this behaviour is connected with single ion magnetism. This is the basic motivation of this proposal.